In the past, the collector consisted of a simple metal electrode, usually made of copper, raised to an appropriate potential (usually that of the anode, which served to accelerate the electrons). However, to increase the efficiency of the tubes it was necessary to produce more sophisticated collectors, called monostage or multistage depressed collectors, formed by several successive electrodes raised to different potentials and therefore electrically insulated from one another.
The production of such collector electrodes poses various problems, these being all the more difficult to solve when the tubes have to be both increasingly powerful and increasingly compact. Among such problems there is the problem of removing the heat produced by the impact of the electrons on an electrode and the problem of secondary electron emission at the electrodes; there is the problem of electrically insulating the electrodes from one another and from the outside; there is the problem of vacuum-sealing the tube, with the related problem of the feed-through of electrical connections from the inside to the outside of the tube in order to take a current or voltage from an internal electrode to the outside of the tube or from the outside to an internal electrode in the tube, and this applies for each of the electrodes of the collector, and also likewise in the case of the other electrodes of the tube (the anode and the cathode).
The solutions adopted for producing these depressed collectors very often use copper electrodes brazed to or shrunk onto parts made of insulating ceramics; the ceramic provides the electrical insulation between electrodes raised to different potentials and in the case of a collector with internal electrical insulations, the ceramic must also transfer the heat flux. The braze provides the mechanical integrity and the vacuum-tightness. These assemblies are complex and costly. Their heterogeneous structure, consisting of ceramics and metal, makes them particularly sensitive to vibrations and thermomechanical stresses. Their performance characteristics are limited, especially as regards efficiency of heat dissipation, permissible operating voltages, compactness, and also sometimes weight (for example for space applications of tubes).
The problems are particularly difficult when producing a multistage collector, but it will be understood that these problems may also exist in the case of insulated electrodes for which it is also necessary to provide, on the one hand, electrical insulation with respect to the rest of the tube and, on the other hand, a voltage or current supply, and finally removal of the heat produced.
The object of the present invention is in particular to produce a tube of improved construction in terms of relationship between the performance obtained and the manufacturing cost.
To do this, the invention proposes, on the one hand, an electron tube having electrodes of novel construction and, on the other hand, a process for manufacturing such a tube.